This invention relates to separating communication signals with an adaptive antenna array. In particular, the present invention relates to separating a desired signal(s) from a jamming signal(s) when the form and direction of the desired signal are unknown.
Adaptive arrays of antenna elements have been applied to improve performance in radar systems for a number of years. More recently, they have been seriously considered for use in communication systems. In monostatic radar, the signal waveform and its direction of arrival are known to the receiver, so most earlier work on adaptive arrays has assumed knowledge of the signal waveform or its direction of arrival. For communications, these assumptions are usually not valid, so limited progress has been made to date in adapting radar results to communication systems.
In an article by the inventor in IEEE Transactions on Aerospace and Electronic Systems, Volume AES-17, No. 2, March 1981, pages 234-247, correction at No. 4, July 1981, page 606, incorporated herein by reference, it is mathematically demostrated that signals incident on an array can be separated using adaptive weights derived from eigenvectors of the cross-correlation matrix of the complex envelopes of the signals received from the antenna ports. The communication problem is modeled in the article along the same lines that S. P. Applebaum modeled the radar problem in IEEE Transactions on Antennas and Propagation, Volume AP-24, No. 5, September 1976, pages 585-598; however, the assumptions that the desired signal is small compared to the interference and that its direction of arrival is known are abandoned. The concept of eigenvector weighting described in the inventor's article has been used differently by W. D. White to separate signals, as described in IEEE Transactions on Antennas and Propagation, Volume AF-24, No. 5, September 1976, pages 670-684 and Volume AP-26, No. 3, May 1978, pages 396-402.